Analysis of variance (ANOVA) of G-BASE sub-surface soil data from 11 urban centres in England and Wales

The G-BASE (Geochemical Baseline Survey of the Environment) programme of the British Geological Survey has collected soil samples throughout a number of urban centres in England and Wales. Surface (0.05m – 0.15m) and sub-surface (0.40m – 0.50m) samples were collected according to a schematic grid pattern, with a density of four samples per square kilometre. At one sample site in each discrete batch of 100 samples, a site sample duplicate was collected. Each of the duplicate pair was subsequently sub-sampled at the sample preparation laboratory to produce a replicate set of four samples for each duplicate site. (Figure 1.)
All samples, including duplicates and replicates, were routinely analysed in the BGS laboratories by wavelength-dispersive X-ray fluorescence, for a total of 16 major and trace elements.
In order to quantify sampling and analytical precision, analysis of variance (ANOVA) was carried out on the replicate data. For sub-surface samples, a total of 50 replicate sets, collected from 11 different urban centres, were used in the ANOVA calculations. The procedures carried out for the sub-surface soils are detailed in this report. Replicate site data is unavailable at present in order to carry out a similar study on surface soils. Table 1 shows the distribution of replicate sites throughout the urban centres.